Cocaine is a powerful stimulant with the potential for creating significant risk for users and for others who share the roadway, workplace, or other site with them. Despite evidence of increasing illicit use of the drug, its effects on performance and thus on safety remain poorly defined. It is a stimulant and stimulants are known to improve performance in a complex task-dose-time relationship. However, accident statistics also indicate negative safety consequences. Safety issues are further complicated because there have been no rigorous examinations of the behavioral symptoms which are associated with cocaine and which could be recognized by an observer. Thus, it is difficult to identify individuals who need to be removed from a particular environment because of cocaine use. The objective of the proposed study are to clarify the nature and extent of performance changes and to identify the symptoms which will enable responsible parties to recognize persons who have used cocaine. Two laboratory experiments with human subjects will 1) examine cocaine effects on the performance of complex tasks as a function of dose level, time of day, and time since dosing, and 2) identify overt behaviors and physical symptoms which are reliably associated with cocaine use. Methods for the proposed study have been developed over the past 15 years during continuous study of alcohol and drugs by the Principal Investigators and colleagues. The experiments will use laboratory tests which are known from that extensive research experience to be sensitive measures of drug effects. The examination of cocaine symptoms will adapt methods from the Los Angeles Police Dept. drug recognition program; the P.I. has been actively involved with that program since its inception.